Differentiation during fig ontogeny suggests opposing selection by mutualists

Dioecy allows separation of female and male functions and therefore facilitates separate co‐evolutionary pathways with pollinators and seed dispersers. In monoecious figs, pollinators' offspring develop inside the syconium by consuming some of the seeds. Flower‐stage syconia must attract pollinators, then ripen and attract seed dispersers. In dioecious figs, male (“gall”) figs produce pollen but not viable seeds, as the pollinators' larvae eat all seeds, while female (“seed”) figs produce mostly viable seeds, as pollinators cannot oviposit in the ovules. Hence, gall and seed figs are under selection to attract pollinators, but only seed figs must attract seed dispersers. We test the hypothesis that seed and gall syconia at the flower stage will be similar, while at the fruiting stage they will differ. Likewise, monoecious syconia will be more similar to seed than gall figs because they must attract both pollinators and seed dispersers. We quantified syconium characteristics for 24 dioecious and 11 monoecious fig species and recorded frugivore visits. We show that seed and gall syconia are similar at the flower stage but differ at the fruit stage; monoecious syconia are more similar to seed syconia than they are to gall syconia; seed and gall syconia differentiate through their ontogeny from flower to fruit stages; and frugivores visit more monoecious and seed syconia than gall syconia. We suggest that similarity at the flower stage likely enhances pollination in both seed and gall figs and that differentiation after pollination likely enhances attractiveness to seed dispersers of syconia containing viable seeds. These ontogenetic differences between monoecious and dioecious species provide evidence of divergent responses to selection by pollinators and seed dispersers.     

Animal dispersal dynamics promoting dioecy over hermaphroditism

Because of the separation of sexual function to male and female individuals, dioecious species have fewer pollen and seed bearers and thus experience disadvantages due to increased aggregation of reproductive function. Because of this disadvantage, models predict that dioecious females must have substantially more than twice the fecundity of hermaphrodites, yet empirical data suggest that female fecundity advantages are commonly much lower. Here, we incorporate animal foraging dynamics--and the heightened dispersal of seeds that may accompany increases in fecundity of dioecious females--into a spatially explicit mathematical model. We focus on the competition for germination sites with varying seed production, seed dispersal ability, and mortality, and we find that preferential foraging on dioecious females reduces the stringent fecundity requirements of dioecy to values in accordance with empirical estimates. This finding contributes to our understanding of the correlation between dioecy and fleshy fruits and highlights the importance of mutualist dispersers to dioecious species.     

How do sessile dioecious species cope with their males?

In terrestrial plants the segregation of male and female reproductions on different individuals results in the seed-shadow handicap: males do not disperse any seed so that the number of local patches reached by seeds is potentially reduced in dioecious populations in comparison to hermaphrodite populations. An analytical model, incorporating a lottery-based recruitment and dispersal stochasticity, was built. The spatially mediated cost of the seed-shadow handicap has been assessed considering the criterions for the invasion of a resident hermaphrodite species by a dioecious species and the reverse invasion, both species having the same demographic parameters but assuming a likely higher fecundity for dioecious females. The reciprocal invasion of a dioecious and hermaphrodite species differing only by their fecundity is never possible. The seed-shadow handicap disappears when the dispersal or survival rate is high enough. This latter point is due to dispersal stochasticity, which allows for the existence of empty patches. A low fecundity and an aggregated seed distribution increase dispersal stochasticity and increase the positive impact of a low mortality rate on the relative competitivity of dioecy and hermaphroditism. Adding a dispersal cost has a comparable effect but also requires higher dispersal rates for the dioecious invasion.     

Inbreeding avoidance and the evolution of gender dimorphism in Wurmbea biglandulosa (Colchicaceae)

How females establish in populations of cosexuals is central to understanding the evolution of gender dimorphism in angiosperms. Inbreeding avoidance hypotheses propose that females can establish and be maintained if cosexual fitness is reduced because they self-fertilize, and their progeny express inbreeding depression. Here we assess the role of inbreeding avoidance in maintaining sexual system variation in Wurmbea biglandulosa. We estimated costs of self-pollination, mating patterns, and inbreeding depression in gender monomorphic (cosexuals only) and dimorphic (males and females) populations. Costs of selfing, estimated from seed set of experimentally self- and cross-pollinated flowers, were severe in both males and cosexuals (inbreeding depression, sigma = 0.86). In a field experiment, intact males that could self produced fewer seeds than both emasculated males and females, whereas seed set of intact and emasculated cosexuals did not differ. Thus, pollinator-mediated selfing reduces fitness of males but not cosexuals under natural conditions. Outcrossing rates of males revealed substantial selfing (t = 0.68), whereas females and cosexuals were outcrossed (0.92 and 0.97). For males, progeny inbreeding coefficients exceeded parental coefficients (0.220 vs. 0.009), whereas for females and cosexuals these coefficients did not differ and approached zero. Differences in coefficients between males and their progeny indicate that selfed progeny express severe inbreeding depression (sigma = 0.93). Combined with inbreeding depression for seed set, cumulative sigma = 0.99, indicating that most or all selfed zygotes fail to reach reproductive maturity. We propose that present sexual system variation in W. biglandulosa is maintained by high inbreeding depression coupled with differences in selfing rates among monomorphic and dimorphic populations.     

Floral biology and pollination mechanisms of four Mexico-endemic Fuchsia species with contrasting reproductive systems

Aims The evolution of the outstanding variation of reproductive systems in angiosperms has been considered an important driver of lineage diversification. Closely related hermaphroditic and dioecious species with biotic pollination provide the opportunity to study and compare traits related to pollinator attraction and their consequences on reproductive components. A higher predictability of pollination syndromes is expected in dioecious species, which are dependent on pollinators, than in self-compatible hermaphroditic taxa. Dioecious species may suffer pollen limitation depending on the quality of floral rewards and the kind and abundance of pollinators, whereas no pollen limitation is expected in hermaphroditic species with autonomous self-pollination. Additionally, in the absence of pollen limitation, more or better seeds are expected in dioecious species, according to the sexual specialization hypothesis.Methods In natural populations of the hermaphroditic Fuchsia fulgens and Fuchsia arborescens and dioecious Fuchsia parviflora and Fuchsia obconica, all endemic to Mexico, we first described flower phenology, flower production and longevity and nectar volume and concentration. Then, we evaluated the correspondence between floral visitors and pollination syndromes. In hermaphrodite plants, we determined the level of herkogamy and the potential for autonomous self-pollination. Finally, we evaluated the effect of pollen limitation on fruit set and seed number and assessed seed germination for all species.Important findings In contrast to our prediction, dioecious species did not show a higher correspondence between pollination syndromes and floral visitors than did hermaphrodites; however, male flowers exhibited a higher correspondence than female flowers. No pollen limitation was detected in dioecious species, for which visitation rate did not differ between male and female flowers. The hermaphroditic F. fulgens showed pollen limitation for seed number, despite the presence of autonomous selfing. Fruit set from autonomous pollination was higher in F. arborescens, which showed a lower level of herkogamy compared with F. fulgens. Finally, dioecious species produced fewer but heavier seeds compared with hermaphrodite species. Although Fuchsia is classified as an outcrossing genus, both hermaphroditic species showed autonomous self-pollination. The heavier but lower number of seeds per fruit in dioecious species may be related to the more efficient resource allocation expected from sexual specialization. This could play an important role in the evolution of dioecy; however, a comparative phylogenetic approach is required to confirm this hypothesis.     

Nutritional Dimorphism in New Guinea Dioecious Figs

The life history of figs (Ficus, Moraceae) involves pollination by specialized insects and seed dispersal by vertebrate frugivores. This three-way interaction raises the possibility of conflict between pollinators and seed dispersers over fig resources. The conflict might be mediated in dioecious figs by the segregation of inflorescences with specialized male and female sexual functions, termed gall figs and seed figs, on separate trees. In dioecious figs, pollinators are intimately associated with gall figs, whereas vertebrate frugivores prefer seed figs and disperse the seeds they contain. Optimal foraging theory predicts that frugivore preference for ripe seed figs is associated with superior nutritional quality when compared to gall figs. We tested this prediction comparing nutrient and mineral properties of ripe figs in 12 functionally dioecious and two monoecious species from New Guinea. Analyses of variance indicated that gall figs contain more fiber and minerals, whereas seed figs contain significantly more carbohydrates and fat. Fruit bats, the primary dispersers of dioecious figs in New Guinea, prefer carbohydrate-rich diets, and from this perspective, seed figs offer a greater nutritional reward than gall figs. More nondigestible fiber in gall figs than seed figs would appear to discourage frugivory. Parallel differences between ripe gall figs and seed figs occur in each independent dioecious lineage whereas nutritional content in monoecious figs is more similar to seed figs. This suggests that sexual dimorphism in nutritional quality might be adaptive and associated with the maintenance of functional dioecy in figs.     

Reproductive implications of combined and separate sexes in a trioecious population of Opuntia robusta (Cactaceae)

Opuntia robusta has hermaphroditic, dioecious, and trioecious populations. To enhance our understanding of this breeding system diversity, we compared the reproductive output of males, females, and hermaphrodites in a trioecious population using field evaluations, controlled crosses, and progeny tests. Unisexuals were fully sterile in one sex function. Hermaphrodites were fully fertile for both functions. Consistent with the sex-allocation theory, unisexuality increased the quality and quantity (in males) of the gametes of the functional sex, relative to those of hermaphrodites, probably explained by maternal and paternal effects. The increase was higher in males than in females, suggesting a more expensive female function. Theoretically, this disproportional increase is required for unisexuals to invade a hermaphroditic population with prior selfing, negligible pollen discounting, and undetectable inbreeding depression, features found in O. robusta, therefore helping to explain dioecious populations. However, in the study population, the actual seed output of females was lower and had a higher variance than that of hermaphrodites, which also reproduce through pollen. Unisexuals are unlikely to be maintained by their actual reproductive output in this pollen-limited environment. Hermaphrodites may persist in this population by producing their seeds autonomously and by reducing interspecific fertilization by prior selfing and ovule discounting.     

Frugivorous birds mediate sex‐biased facilitation in a dioecious nurse plant

Abstract. Facilitation by dispersal occurs if the nurse plant acts as a focus which is actively selected by seed dispersers and enhances the fitness of the facilitated plant. Sex‐biased facilitation may be produced if seed dispersers tend to concentrate the seeds under female, fruit‐bearing plants of dioecious species more often than under conspecific males. Juniperus sabina is a dioecious shrub with a prostrate growth form from Mediterranean high mountains that modifies many microhabitat characteristics related to seedling establishment and survival. Soil water availability, maximum soil temperature in summer, organic matter and total nitrogen content, were different on open ground as compared with beneath J. sabina shrubs, irrespective of its sex. Other studied characteristics such as soil bulk density and soil compaction after rain did not differ between the microhabitats considered. Some species, such as Juniperus communis, Pinus nigra, Helleborus foetidus and Euphorbia nicaeensis, are spatially associated to J. sabina shrubs, strongly suggesting a facilitative role. The anemochorous P. nigra and myrme‐chorous H. foetidus and E. nicaeensis did not associate preferentially to any sex of J. sabina. Only J. communis, an endozoochorous species sharing the same bird dispersers as J. sabina, presented a female‐biased spatial association with the nurse plant. Seed dispersal mediated by birds attracted by the fruit‐rewarding females of J. sabina explains the sex‐biased spatial pattern of Juniperus communis.     

Spatial seed and pollen games: dispersal,sex allocation,and the evolution of dioecy

The evolutionary forces shaping within‐ and across‐species variation in the investment in male and female sex function are still incompletely understood. Despite earlier suggestions that in plants the evolution or cosexuality vs. dioecy, as well as sex allocation among cosexuals, is affected by seed and pollen dispersal, no formal model has explicitly used dispersal distances to address this problem. Here, we present a game‐theory model as well as a simulation study that fills in this gap. Our model predicts that dioecy should evolve if seeds and pollen disperse widely and that sex allocation among cosexuals should be biased towards whichever sex function produces more widely dispersing units. Dispersal limitations stabilize cosexuality by reinforcing competition between spatially clumped dispersal units from the same source, leading to saturating fitness returns that render sexual specialization unprofitable. However, limited pollen dispersal can also increase the risk of selfing, thus potentially selecting for dioecy as an outbreeding mechanism. Finally, we refute a recent claim that cosexuals should always invest equally in both sex functions.     

食果动物与被取食植物的相互关系:协同进化?

在种子传播过程中动植物是否存在协同进化关系一直是争论的焦点。有观点认为,植物通过食果动物对其种子的传播可能获得逃避种子捕食者、占据新的生境斑块和基因流动等好处,而动物通过消化果肉获得营养和能量作为回报,动植物彼此相互作用,进而可能建立协同进化关系。动植物之间还可能发生在种、属或科水平以上的多物种的多配协同进化,或者通过关键种的协同进化来带动其他食果动物和植物相关性状的进化。“果肉防御假说”则认为果肉原本是保护种子的防御组织,后来才进化成为吸引食果动物以促进种子传播的物质。然而,食果动物和植物一对一的协同进化的例证并不多见;适合种子萌发和生长的环境在时空上难以确定;食果动物和植物的进化速度不一致;植物与种子传播者的选择压力存在着高度的不对称和不平衡,加上环境因素的重要影响,这种选择压力受到极大的限制而有可能变得不显著。种子传播中动植物在进化意义上的关系尚需进一步研究。未来研究应对食果动物和植物关系的复杂性和多样性有足够的认识。通过对系统发育中相联系的不同种的动植物关系的比较研究来揭示动植物关系对物种分化的影响,有可能为检验食果动物和植物之间的协同进化关系提供新的证据。食果动物传播种子对植物群落动态变化的影响、动植物关系和生物多样性保护等仍将是该领域研究的热点。     

How much Dillenia indica seed predation occurs from Asian elephant dung?

Elephants are thought to be effective seed dispersers, but research on whether elephant dung effectively protects seeds from seed predation is lacking. Quantifying rates of seed predation from elephant dung will facilitate comparisons between elephants and alternative dispersers, helping us understand the functional role of megaherbivores in ecosystems. We conducted an experiment to quantify the predation of Dillenia indica seeds from elephant dung in Buxa Reserve, India from December 2012 to April 2013. Using dung boluses from the same dung pile, we compared the number of seeds in boluses that are a) opened immediately upon detection (control boluses), b) made available only to small seed predators (<3 mm wide) for 1–4 months, and c) made available to all seed predators and secondary dispersers for 1–4 months. Using a model built on this experiment, we estimated that seed predation by small seed predators (most likely ants and termites) destroys between 82.9% and 96.4% of seeds in elephant dung between the time of defecation and the median germination date for D. indica. Exposure to larger seed predators and secondary dispersers did not lead to a significant additional reduction in the number of seeds per dung bolus. Our findings suggest that post-dispersal seed predation by small insects (<3 mm) substantially reduces but does not eliminate the success of elephants as dispersers of D. indica in a tropical moist forest habitat.     

Sex determination in the androdioecious plant Datisca glomerata and its dioecious sister species D. cannabina.

Datisca glomerata is an androdioecious plant species containing male and hermaphroditic individuals. Molecular markers and crossing data suggest that, in both D. glomerata and its dioecious sister species D. cannabina, sex is determined by a single nuclear locus, at which maleness is dominant. Supporting this conclusion, an amplified fragment length polymorphism (AFLP) is heterozygous in males and homozygous recessive in hermaphrodites in three populations of the androdioecious species. Additionally, hermaphrodite x male crosses produced 1:1 sex ratios, while hermaphrodite x hermaphrodite crosses produced almost entirely hermaphroditic offspring. No perfectly sex-linked marker was found in the dioecious species, but all markers associated with sex mapped to a single linkage group and were heterozygous in the male parent. There was no sex-ratio heterogeneity among crosses within D. cannabina collections, but males from one collection produced highly biased sex ratios (94% females), suggesting that there may be sex-linked meiotic drive or a cytoplasmic sex-ratio factor. Interspecific crosses produced only male and female offspring, but no hermaphrodites, suggesting that hermaphroditism is recessive to femaleness. This comparative approach suggests that the hermaphrodite form arose in a dioecious population from a recessive mutation that allowed females to produce pollen.     

THE MAINTENANCE OF GYNODIOECY AND ANDRODIOECY IN A METAPOPULATION

Males and females are at a selective disadvantage relative to hermaphrodites (cosexuals) in species with a colonizing habit, as only cosexuals are able to establish new colonies on their own. The implications of this disadvantage are assessed by means of a computer model of metapopulation dynamics, in which individual colonies are established through different rates of immigration and suffer different rates of local extinction. Results are given for simulations of an island model, a stepping-stone model, and for a partial analysis of the island model with simplifying assumptions. It is shown that: (1) unisexual frequencies in a metapopulation can be reasonably approximated by a linear function of the logarithm of the ratio of the immigration rate to the colony extinction rate; (2) metapopulation dynamics favor the maintenance of females (gynodioecy) over males (androdioecy) with cosexuals when they would otherwise be equally likely in a panmictic situation; (3) the way in which extinction and immigration rates affect unisexual frequencies at metapopulation equilibrium interacts with whether sterility is determined by a dominant or a recessive allele; and (4) unisexual frequencies are affected in a qualitatively similar way by the dynamics of a metapopulation when cosexuals are self-incompatible to when they are self-compatible, although only in the former case are high frequencies of unisexuals maintained when extinction and colonization rates approach the threshold at which the metapopulation goes extinct. These results are discussed with reference to existing data from species with nuclear male or female sterility.     

Origins of variance in seed number and mass: interaction of sex expression and herbivory in Lomatium salmoniflorum

Summary As in many plant species, Lomatium salmoniflorum (Umbelliferae) individuals produce many flowers, only a subset of which produce mature seeds that escape seed parasitism and enter the seed bank. The interrelationships between the timing and number of flowers produced, sex expression, seed set, and seed parasitism were studied for their direct and indirect effects on the numbers and masses of viable seeds produced by individual plants. In a sample population of 369 plants that produced 161 386 flowers, 76% of the plants produced some hermaphroditic flowers. The percentage of hermaphroditic flowers increased significantly with the total number of flowers produced by a plant. Seed set was 65–90% in plants producing >600 flowers, but was highly variable in plants producing fewer flowers. Hand-pollinated plants showed the same pattern of seed set, suggesting that variable seed set in small plants may result from insufficient resources for seed development. The majority of schizocarps was produced by only 12% of the plants. Parasites killed 24.5% of the seeds prior to dispersal. Another 14.5% of the seeds lacked endosperm. Hence, the initial 161 386 flowers, which included 25874 hermaphroditic flowers each capable of producing two seeds, produced 42 468 seeds of which an estimated 25906 entered the seed bank as undamaged seeds with fully developed endosperm. Path analysis indicated that the number of hermaphroditic flowers on a plant and the percentage of seeds attacked by seed parasites had the greatest direct effects on the number of viable seeds entering the seed bank. The date at which a plant began flowering and the percentage of flowers setting seed had smaller or only indirect effects on viable seed production. Mean seed mass for plants was not significantly related to any of the factors that affected seed number, but little of the variance in seed mass occurred among plants. Masses of intact seeds in the population ranged 9-fold in both 1987 and 1988. Thirty-five percent of the variance was among seeds within umbels, 46% was among umbels within plants, and only 19% was among plants. The large variation among umbels within plants resulted from a seasonal pattern in which seeds from umbels produced late in the spring had lower mean seed masses than seeds from umbels produced early in the spring. Overall, the results indicate that both direct and indirect interactions between number of flowers, the date of initiation of flowering, seed set, and seed parasitism affect the number of viable seeds entering the seed bank. These interactions strongly bias viable seed output to a small minority of plants that produce many seeds with a wide range of masses over the growing season.     

A Reconsideration of the Reproductive Biology of the Atlantic Forest in the Volta Velha Reserve

Published species lists that include breeding system designations of vascular plants are rare in the primary literature and, thus, can be potentially valuable sources of information for comparative studies. The published list for vascular plants in the Volta Velha Reserve suffered from a number of errors, notably applying the designation of monoecious to all species with imperfect flowers. Here, I reconsider the breeding systems for 97 woody vascular plant species. The majority of species initially categorized as monoecious are found to be hermaphroditic. I then examine the relationship between breeding system and numbers of individuals in a 1 ha plot. The mean number of individuals was marginally higher in dioecious than hermaphroditic and monoecious species combined. Furthermore, although only 28% of the species were characterized as possessing a dioecious breeding system, 42% of the individuals encountered belonged to a dioecious species. These results suggest that dioecious species can, at least under certain circumstances, overcome the reductions in the number of seed-bearing individuals and mate assurance that accompany possessing spatially segregated sexes.     

The Role of Arboreal Seed Dispersal Groups on the Seed Rain of a Lowland Tropical Forest1

Most tropical plants produce fleshy fruits that are dispersed primarily by vertebrate frugivores. Behavioral disparities among vertebrate seed dispersers could influence patterns of seed distribution and thus forest structure. This study investigated the relative importance of arboreal seed dispersers and seed predators on the initial stage of forest organization–seed deposition. We asked the following questions: (1) To what degree do arboreal seed dispersers influence the species richness and abundance of the seed rain? and (2) Based on the plant species and strata of the forest for which they provide dispersal services, do arboreal seed dispersers represent similar or distinct functional groups? To answer these questions, seed rain was sampled for 12 months in the Dja Reserve, Cameroon. Seed traps representing five percent of the crown area were erected below the canopies of 90 trees belonging to nine focal tree species: 3 dispersed by monkeys, 3 dispersed by large frugivorous birds, and 3 wind‐dispersed species. Seeds disseminated by arboreal seed dispersers accounted for ca 12 percent of the seeds and 68 percent of the seed species identified in seed traps. Monkeys dispersed more than twice the number of seed species than large frugivorous birds, but birds dispersed more individual seeds. We identified two distinct functional dispersal groups, one composed of large frugivorous birds and one composed of monkeys, drop dispersers, and seed predators. These groups dispersed plants found in different canopy strata and exhibited low overlap in the seed species they disseminated. We conclude it is unlikely that seed dispersal services provided by monkeys could be compensated for by frugivorous birds in the event of their extirpation from Afrotropical forests.     

Mating system contributes only slightly to female maintenance in gynodioecious Geranium maculatum (Geraniaceae)

Gynodioecy, the co-occurrence of female and hermaphroditic individuals within a population, is an important intermediate in the evolution of separate sexes. The first step, female maintenance, requires females to have higher seed fitness compared with hermaphrodites. A common mechanism thought to increase relative female fitness is inbreeding depression avoidance, the magnitude of which depends on hermaphroditic selfing rates and the strength of inbreeding depression. Less well studied is the effect of biparental inbreeding on female fitness. Biparental inbreeding can affect relative female fitness only if its consequence or frequency differs between sexes, which could occur if sex structure and genetic structure both occur within populations. To determine whether inbreeding avoidance and/or biparental inbreeding can account for female persistence in Geranium maculatum, we measured selfing and biparental inbreeding rates in four populations and the spatial genetic structure in six populations. Selfing rates of hermaphrodites were low and did not differ significantly from zero in any population, leading to females gaining at most a 1–14% increase in seed fitness from inbreeding avoidance. Additionally, although significant spatial genetic structure was found in all populations, biparental inbreeding rates were low and only differed between sexes in one population, thereby having little influence on female fitness. A review of the literature revealed few sexual differences in biparental inbreeding among other gynodioecious species. Our results show that mating system differences may not fully account for female maintenance in this species, suggesting other mechanisms may be involved.     

棕果蝠取食对两种榕树种子萌发行为的影响

在实验室利用聚果榕（Fieus racemosa）和对叶榕（Fieus hispida）成熟的果实饲喂笼养棕果蝠（Rousettus leschenaulti）,比较了不同处理的3组种子的萌发行为：（1）棕果蝠粪便中的种子;（2）被吐出的果渣中的种子;（3）成熟果实中的种子（对照）。棕果蝠取食行为显著影响了两种榕树种子的萌发过程,3种不同处理的种子萌发过程及最终萌发率（GP）之间都存在显著的差异。聚果榕种子经过棕果蝠消化道后GP显著降低,而对叶榕种子的GP显著提高。棕果蝠粪便中的聚果榕种子萌发开始（GS）和最短萌发时间（Tmin）均比对照种子延迟了2d,但其粪便中的对叶榕种子G5比对照种子提前了1d,Tmin提前了2d;与之相似,前者种子萌发比果实中种子提前2d达到萌发总量的50％（T50）,但后者没有改变T50。不同种榕果果渣中的种子萌发行为也有重大差异：聚果榕果渣中种子的Tmin和T50均比对照种子延迟1d,GS没发生改变;而对叶榕果渣中种子的Tmin比对照种子提前了3d,GS提前1d,T50没有改变。棕果蝠取食两种榕果后在飞行过程中排泄,进而有效的散布种子;而且通过消化明显改变了种子萌发行为,使种子萌发类型更为多样,增加了种子在不同时空条件下萌发的可能性。     

Diversity of seeds captured by interception exceeds diversity of seeds deposited in traps

Seed dispersal, a key process in terrestrial landscapes, is increasingly important in the face of habitat fragmentation and global climate change. Seed dispersal is also notoriously difficult to characterize, especially in species rich and spatially complex tropical forests. We contrasted assemblages of biotically dispersed seeds collected from four sites using two methods: deposition into seed traps and interception by the capture of frugivorous birds. We also compared seed deposition and interception with local fruit production. Species accumulation curves for seeds deposited in seed traps began to level off sooner than curves for seeds collected from birds captured in mist nets, and extrapolation showed significantly greater estimated species richness for seeds collected from birds than for those deposited in traps. Assemblages from birds and from traps at each site were quite different, with an abundance‐based similarity index of 0.64; this dissimilarity increases if bat‐dispersed seeds are included in the analysis. Common bird‐dispersed species were retrieved from both mist‐netted birds and from seed traps, but numerous locally fruiting understory species were recovered only from birds. We conclude that the sampling of seeds carried by birds provides a valuable complement to other methods of studying seed dispersal in species‐rich tropical forests by revealing relationships between specific dispersers and their seed plants and by creating a more complete account of species diversity of seeds being transported at a given site.     

Frugivory and Seed Fate in Bursera inversa (Burseraceae) at Tinigua Park,Colombia: Implications for Primate Conservation1

The large ateline primates are efficient seed dispersers in Neotropical forests and hunting is driving their populations to extinction, but we do not know whether other frugivores could substitute primates in their ecological role as seed dispersers. In this study we test this possibility using a potential keystone species (Bursera inversa) at Tinigua Park, Colombia. This plant species allows us to compare seed removal rates between emergent, isolated trees, without primate visitors and trees with connected crowns. We used traps to estimate fruit production and seed removal rates in six different trees, and fruiting trees were observed during 2 yr to quantify the number of seeds manipulated by different animal species. We carried out seed predation experiments to test if seed removal by predators was affected by distance or density effects. We found that the most productive trees attracted more visiting species and seed removal rates differed among trees, the lowest corresponding to trees without primate access. Seed removal rates from the ground by predators were not higher below parental trees than away from them, but the distribution of saplings in the forest suggests that seed dispersal is advantageous. Although it is likely that the effect of primate extinctions will vary depending on tree species traits, conserving the populations of primate seed dispersers is critical to maintain the ecological processes in this forest.